Sounds like this is an awesome piece of work!

Since the patch is obviously a very large piece and will be hard to
review, may I suggest releasing the new engine as a standalone package
and spreading the word, so that people can stress-test it?  By the time
2.7 is ready to release, if it has had considerable exposure to the
public, that will help acceptance greatly.

The Unicode script identification might not be hard to add to
unicodedata; maybe Martin can do that?